Helicopter gunships have conducted strikes on the northern Iraqi city of Tikrit, the Iraqi military says, according to BBC News.

The attacks come amid reports of a major offensive to retake Tikrit from Isis-led Sunni militants, who control large parts of north and west Iraq. The news came hours after the US confirmed it was flying drones in Iraq, to protect US personnel on the ground.

The air strikes targeted Sunni insurgents attacking troops who have established positions in a university campus to the north of Tikrit, military spokesman Lt-Gen Qassim al-Moussawi was quoted as saying by the Associated Press.

Tikrit, the birthplace of former Iraqi leader Saddam Hussein, is a mainly Sunni city which fell to militants led by Isis - the Islamic State in Iraq and the Levant - in recent weeks.

Unconfirmed reports say that thousands of troops are advancing on the city from nearby Samarra, backed by aircraft, tanks and bomb disposal units.